Modeling of cryogenic cracking behavior of tight sandstone under confinement

Abstract

Stimulation is a must for commercial development of tight sandstone hydrocarbon reservoirs. Cryogenic fracturing using liquid nitrogen (LN) is a promising clean technique for efficiently stimulating reservoir rocks given its waterless nature. We developed a fully coupled thermo-mechanical (TM) model that incorporates strain-based damage theory for simulating LN cryogenic cracking in tight sandstone. Particularly, the compressive and tensile strengths, Young’s modulus, and thermal expansion coefficients and conductivity are designated as dynamic functions of the damage variable during the TM coupling process. Then the initiation, propagation, and cessation of multiple cracks from a borehole within a 2D heterogeneous tight sandstone plate were systematically scrutinized. Cryogenic cracks are found to emerge in short and long forms. In accordance with experiments, multiple long cracks emanate radially from the borehole along the maximum horizontal stress direction. In the investigated parameter ranges, the fracture morphology, including numbers, lengths, and coverage, is susceptible to changes in in-situ stress, Young's modulus, and thermal conductivity, but relatively insensitive to the variations of heat transfer coefficient and sandstone density. These results deepen our understanding of cryogenic shock on tight sandstone and provide a theoretical reference for designing cryogenic treatment operations.